Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
3L~5722~
METHOD FOR SORTIN~ RADIOACTIVE WASTE
Summary_of the Invention
This invention reLates to a method for examining dry mate-
rial, co~ponents of which may have a low level of radioactivity,
to sort the radioactive components from the nonradioactive compo-
nents. It comprise9 the ~teps of placing of material in a first
detection station where radiation above a predetermined level can
be detected and then removing the components from which the radl-
ation is emanating. The remainder of the material is then con-
veyed to a second detection station where means are provided for
detecting radiation above a second predetermined level. The com-
ponents of the material which is detected as having radiatio~
which is a level above the second level i3 then removed. The
remaining components are then placed iQ a conta~ner and the con-
tainer is delivered to a third radiation detection station where
radiation emanatin8 from the container which is above a predeter-
mined level i9 detPcted. If no radiation i~ detected a~ emanat-
in8 from the eontainer then the container and the material there-
in are d~sposed of as nonradioactive.
293-3
-- 1 --
~257224
Back ~ Invention
This invention relate9 to a method for sortin~ radioactive
waste having a low level of radioactivity and more particularly
to a method which i9 inexpensive and efiic~ent.
Th~ waste present~ problems due to the danger of in~ury to
those that may come into contact with it notwith~tandin~ the fact
that only low levels of radloactivity are present. Thus, while
Lt is generally acknowledged that exposure to low level3 of radl-
ation over long period~ of time i9 hazardouq, there i9 inadequate
information a~ to what levels of radiation are 9afe over a long
term of exposure. Typically, industry ~tandards have set flve
REM per year a~ the maximum exposure to which a human should be
sub~ected. A REM i~ a Roengeen Equivalent Man, a well known
mea~ure of expo~ure to radiation.
The radlation arises from the emi~sion of alpha and bata
particles as well as the emission of gamma ray~, The beta parti-
cles and gamma ray~ pre~ent more of a hazard from external expo-
sure than the alph~ particleq. Thi~ is becauqe the alpha parti-
cles which comprise helium nuclei are charged and haYe a rela~
tively high ma~s. Consequently, they can be stopped by a materi-
al ~uch as a ~hee~ of paper.
Beta pa~ticle~, which are free electrons, have substan-
tialLy 8reater penetrating power than alpha particle~. Neverthe-
le99, they can be ~topped by a few millLmeters of a metal such a~
aluminum.
Gamma rays, however, have unli~ited range ~ince they have
the abi~ity to make deep penetrations of material. They can only
be minimized by a ~ubstan~ial thicknes~ of a material ~uch a~
lead.
- 2 -
~ 2~ 4
As n~clear facilities tend to proliferate, the disposition
of waste has become an increa~ing problem. ThlQ i9 because buri-
al 3i~es are a~ a premium and because huge quantlties of waste
are generated by the3e facilities. Wa~te which 19 highly active,
such a~ spent nuclear fuel or the like, i~ buried after being
placed in shielded cani~terQ. However, because of the difficulty
of obtaining burial sites, it is worthwhile to examine waste
having a Low activity to remove the nonactive component~. This
reduces the quantity of material which must be buricd. Typical-
ly, waste having low activity include~ paper, fabrics, boots,cl~thing, tools and various miscellany which can normally be
expected to be used and di~po~ed of $n the operation of a nuclear
facility. The waste may be collected in bag~ at the facillty.
It may include itemY that emlt alpha and beta particle3 as well
as gamma ray~. Other item~ may not be radioactive. Occa~ional-
ly, an effort may be made to sore item~ of high value such as
tool~ and the like. However, this effort is u~ually discouraged
because of the risk to per~onnel of radiation contamina~ion.
A~ a result, lar~e quantities of waste are ~enerated for
burial becau~e they are believed to have low levels of radioacti-
vity notwithstanding the fact that they have no radioactive con-
tent or that the material~ which are radioactive can be readily
se~regated from the non-active waste. Conqequently, much more
materlal ls being buried than i~ neces~ary.
The present invent~on relates ~o a method for segregating
the componen~s of radloactive wa~te having an activity above
predetermined level~ from the remainder of the wa~te. The me~hod
re~ults in a sub~tantial reductlon in the volume of radioactively
contaminated waste that need be buried,
-- 3 --
~2S722~
The method is operable on an almost continuous basLq.
Further, it rely9 on detector~ whlch generate alarm~ when radio-
activlty above predetermined level~ is detected. It Ls especial-
ly advantageouY Rince lt can be operated by per~on~ of relatlvely
low Ykill.
Further, ln ttte event of mechanical fallure, those por~
tlons of the ~y`stem which are operative can contlnue to operate
whlle replacement part~ are obtained for those portions which
have failed.
Brief Description of the DrawingR
Flgure 1 is a schematlc drawing showlng the steps which
comprise the method for sorting radloactive wa3te in accordance
with a presently preferred form of the invention.
Detailed_Descrlption of the Pr ferred EmbodLment
Preferably, wa~te from variouR parts of a power plant or
other faeillty i9 collected, placed in ~uitable containers such
as plastic bags and surveyed for radioactivity. The bags may be
small enough so tha~ when they are filled they can be readily
handled by maintenance people.
-- 4
'3L25~7Z24
The filled bags are dellvered to a station where they are
examined to determine their radloactivity. Bags that display a
predetermined level of activity may be di3po~ed of a3 radio-
active.
The remainLn8 bag~ are delivered to ~n in~pection station
~here their contents are emptied so that ~*~ components can be
inspected by radiation detectorq. During thLs Lnterval items
which are considered to be of value such as tool~, laboratory
equipment, clothing and the like can be separated from the other
lG waste and saved.
At an intermediate portion of the method the wa~te is
shredded to a relatively small size so that radiation emanating
from it can be readily detected as it passes under radiation
detectors~
Finally, the shredded material is collected in sultabl~
containers such a~ bags or boxe~ and compacted. The compacted
material i3 transferred to a last detector for final examina-
tion. If no radlation abo~e a predetermined leveL i~ detected
then the container can be disposed of as clean wa~te. On the
20 other hand, ~f radiation above the predetermined level i8 detec-
ted then the con~ainer is disposed of as radioactive waste.
Since most of the waste which is collected at nuclear
facilitie3 is not radioactive, the ability to segregate the non-
radioactive component~ from the radioactlve components re~ult3 ln
a ~ignificant and dramatLc reduction in the volume of wa~e which
mus~ be treated as radioactive.
In view of the fact that di~po~al site~ ~or radioartive
waste are at a premium, the ability to r~duce the volume of radi~
oactive waste significantly make3 an important contr~bution eo
~0 the nuclear power plant indu~try.
~257~24
Referrin8 now to the drawing in detail, a ba~ 10 i8 illu~-
trated. The bag may be made of any convenient material such a
that which iq readily available commercially a~ tra~h bags.
Typically, such bag~ should be s~all enough ~o be ea~ily handled
when they are full. They are placed in receptacle~ at various
locations in the nuclear facility ~o that wa~te whLch may have a
low level of radioactivity can be placed in them by the plant
per30nnel. The waste may come from variou9 part9 of a power
plant such as the offices, shops, laboratorie~ and work areas~
The wa~te may compri~e wrappers, papers, tool~, shoes, clothing,
metal parts, fittings and the like.
After bein8 collected, a filled bag 10 is given a prelimi-
nary examination for radiation emis3ion at a suitable station
t4. The examination may be conducted by suitable do~e rate
meter3 of a type well known. If the radiation exposure hazard
from a bag i~ greater than a predeter~ined level ~uch as two
~illiroentgens per hour, the bag i~ considered to be a radiologic
hazard to be di~po8ed of without further action along with other
hazardou~ substance3~
If the ba8 10 does not cause the do~e rate me~er to exceed
the predetermlned level, it is considered to have a low enough
level of radioactiviey to ha~e ~ts contents examined. In thi~
4 frega ~ itfiS removed to ~ ~de~ radlation detection ~tation 18.
The *~een~ s~ation may be a suitably ~hlelded sorting table of
the eype which includeg radiation detectors and which i3 con-
structed to minimize ~he rad~ation hazard to whl~h operatin~ per-
30nnel mi~ht be exposed.
- 6 -
~5'722~
~7_ 52,563
A suitable table may take the form of the Sortirg Table
which is disclosed in U.S. Patent 4,599,513 issued July ~,
1~84, entitled ENCLOSURE FOR SORTING RADIOACTIVE MATERI~L
to Anthony J. Prisco and Alfred N. Johnson. At the sorting
table the operating personnel open the bag and the contents
of the bag are individually examined for ~eta particle
contamination. A suitable device for measuring beta
contamination is a gas proportional detector. Gas propor-
tional detectors are well known in the art and need not be
described in detail. Preferably, the gas proportional
detector is arranged to detect surface contamination levels
in beta particle disintegrations per minute per 100 square
centimeters. Disintegrations per minute per 100 square
centimeters is the standard unit of measurement for surface
Contamination.
Should an item which was contained in the bag exhibit
beta surface contamination in excess of a predetermined level,
an alarm is energized. The operator can remove the item
from detection station 18 for treatment as radioactive waste.
Those components of the waste which do not energize
the alarm are then transferred to a second radiation detection
station 22 by the operating personnel.
The second radiation detector station 22 may comprise a
suitable conve~or 26 which delivers the articles of waste
25 frcm the ~ radiation detection station 18 to a shredding
device 30. The shredder 30 shreds the waste so that the size
of the items contained is reduced to a relatively small
uniform size. After passin through the shredder 30, the
shredded waste is spread to asubstantially uniform thickness
30 and mo~ee on a conveyor 34 past suitable beta particle and
gamma ray detectors 34a.
~L25~22~
8 52,563
The beta particle detectors are typically gas
proportional detectors of a type which are well know in the
art. They may be arranged to energize an alarm when they
detect surface contamination levels in excess of
predetermined levels. This is duplicative to some extent of
the detection level which is available at station 18.
However, it tends to serve as a reinforcement of the
reliability of the first detector.
The gamma ray detectors may comprise scintillation
detectors of a type which is well known in the art. The
scintillation detectors are arranged so that they energize
an alarm if surface contamination in excess of predetermined
gamma contamination levels are detected.
Since beta particles have a low penetrating power,
the waste is overturned and redistributed during the course
of the examination so that beta particles which are emitted
from hidden surfaces can also be detected by second
radiation detectors.
A suitable device for conveying the waste to a
shredder, shredding and overturning the material as it is
being examined is disclosed in U.S. Patent 4,679,738 issued
July 14, 1987 entitled CONVEYOR FOR SORTING RADIOACTIVE
WASTE AND METHOD OF USING THE SAME to Anthony J. Prisco and
Alfred N. Johnson.
If any components of the waste which is being
examined exhibits activity in excess of predetermined
surface contamination levels, the alarm is energized to
alert the operator to remove the contaminated components
from the conveyor for disposal as radiologically active
waste.
~S~
The component~ which do not energize the alarm are per-
mitted to contlnue alon~ the conveyor 34 where they are dispensed
into a ~uitable contaLner 36.
Preferably, the container 36 i9 compriqed of an inexpen-
sive light weight material which can be readily manufactured and
handled. Succes~ful reRult~ have been achieved with plastic
trash bags and ordinary cardboard boxe~. The ba8s and boxe~ are
usually strong enough to ~upport the shredded waste. Becau~e of
the nature of beta particle~, to the extent thac such particle8
10 remain in the waste, they are stopped by the container 36. How-
ever, due to the fact thac the gamma rays can pass through the
containers, they are checked again for gamma radiation.
In view oi the low likelihood that gamma radiation is con-
tained in the surviving waste, it i5 worthwhile to compact the
material into the container. This greatly lncreases it~ den~ity
without increa~ing its volume. Consquently a large masq of mate-
rial can be examined for 8amma ray emissLon at one time. In thi~
regard, a suitable compacto~ 38 i8 provided. The compactor can
be of any sLze or model that is commercially available in the
art. A suitable compactor ig available from Union Environmental
Divi~ion of Union Corporation in Old For~e, Pennsylvania.
The container 36 of compacted wa~te is the~ ~ ~ered to a
radiation detection sta~ion 40. The radiation
detection station may comprise a de~ec~or for meaquring 8amma ray
contamination. To thi~ ex~ent, it may comprise several qclntiL-
lation detectors which are arran8ed ~o that they can detect gamm~
contamination at a predetermined level of radioac~i~ity.
~L257224
52,563
If gamma ray contamination in excess of a
predetermined level is detected, the contents of the
container are treated as radioactive waste and are disposed
of accordingly. However, if that level of contamination is
not detected, then the container can be disposed of with the
ordinary non-radioactive waste which is generated by the
nonradiologically controlled parts of the facility.
A typical device which can be used for the
detection of gamma radiation emanating from a container of
compacted ma-terial is disclosed in U. S. Patent ~,658,142
issued April 14, 1987 to Alfred N. Johnson and Anthony J.
Prisco which is entitled METHOD AND APPARATUS FOR DETECTING
RADIATION IN A CONTAINER.
Thus, what has been described is a method for
sorting waste which has radioactive components and to remove
those components by a quick and efficient system. It
results in a significant reduction in the volume of material
that must be disposed of as hazardous.
Since the volume of radioactive material is
substantially reduced, it can be transferred to burial sites
in significantly smaller quantities and at lesser cost so
that the rate at which the burial sites are filled is
dramatically reduced.
While the invention has been described with
respect to a particular form thereof, it is apparent that
other forms should be obvious to those skilled in the art.
Thus, the scope of the invention should not be limited by
the foregoing, but rather, only by the scope of the claims
appended hereto.
~, .
